The present invention relates to a mounting device for mounting an exhaust gas recirculation valve located in a reflux passage of exhaust gas of an internal combustion engine and others.
FIG. 6 is a cross sectional view showing a conventional mounting device for mounting an exhaust gas recirculation valve. Referring to the drawing, a valve housing 1 includes an exhaust gas inlet 2 that communicates to an exhaust system (not shown) of an engine acting as an internal combustion engine, an outlet 3 that communicates to an air intake system (not shown) of the engine, and a passage 4 that is interposed between the outlet 3 and the mentioned inlet 2. In the passage 4, a valve seat 5 is press-fitted. Reference numeral 6 designates a valve rod that passes through a bush 7. A valve 8 that comes in contact with or separates from the valve seat 5 is mounted at a lower end portion of the valve rod 6. Numeral 9 designates a holder for preventing a deposit from entering the bush 7. Numeral 10 designates a spring holder that is given an upward impetus by coil spring (in other words, return spring) 11. A through-hole 12 is formed in a central portion of the spring holder 10. A tip portion 6a of the mentioned valve rod 6 is caulked and fixed into the through-hole 12. Due to this caulking, the valve 8, which is mounted at the lower end portion of the valve rode 6, is given an impetus at all times in the direction of closing the valve with respect to the valve seat 5. Furthermore, numeral 13 designates a cooling water passage for cooling a valve body and a motor, as described later. Numeral 15 designates a cap for sealing in an airtight manner.
Numeral 20 designates a stepping motor body serving as a stator assembly including a rotor portion described later. A spacer 21, which prevents water from entering the stepping motor body 20, is secured by a clamp screw 23 via a rubber ring 22 at a lower portion of the stepping motor body 20. A motor bush 25 for holding a motor shaft 24 is disposed in a central opening of the spacer 21. A spring holder 26 is connected to a lower end portion of the motor shaft 24. Numeral 28 designates a spring, that is, an assist spring that is disposed between the spacer 21 and the spring holder 26, and gives an impetus to the motor shaft 24 in the direction of opening the valve 8.
Numeral 30 designates a bobbin around which a coil 31 is wound, and a yoke 32 and a yoke 33 providing a magnetic passage are formed about an outer periphery of the bobbin 30. Numeral 34 designates a terminal, which is electrically connected to the coil 31 and forms a connector section along with a motor housing 35. Numeral 36 designates a plate for shielding two coil parts in terms of magnetism. Numeral 37 designates a plate for preventing resin from coming into an inner periphery of the coil part at the time when the motor housing 35 is molded exteriorly.
Numeral 40 designates a magnet. Numeral 41 designates a rotor, which holds the magnet 40, and at an inner periphery portion of which a female-threaded part 41a engaging with a male-threaded part 24a of the motor shaft 24, and a stopper 41b in an axial direction for the motor shaft 24 are formed. Numeral 42 designates a bearing mounted on both ends of the rotor 41. Numeral 24b designates a stopper part provided at the motor shaft 24.
The stepping motor body 20 as constructed above is mounted onto the mentioned valve housing so as to be coaxial by means of a fixing screw 44.
In addition, relation between the rotor 41 and the motor shaft 24 is now described. A lower half of the motor shaft is a plate-like member 24c, which includes a shaft in the direction of the motor shaft 24 at the center part thereof. The plate-like member 24c is inserted through a substantially square through hole of the motor bush 25 to be prevented from rotation. Further, the plate-like member 24c is held so as to be capable of moving in an axial direction thereby enabling the motor shaft 24 to move in up and down direction. By the screw-engagement between the male-threaded part 41a of the rotor 41 and the female-threaded part 24a of the motor shaft 24, the rotation of the rotor 41 causes the motor shaft 24 to move up and down. The axial stopper 41b is a protrusion provided in a recess at an inner periphery of the rotor 41. The axial stopper 41b comes into contact with the plate-like member 24c of the axial stopper 41b at an upper dead point of the motor shaft 24 due to the rotation of the rotor 41. The rotor 41 is prevented from further rotation in one direction beyond the upper dead point, thereby the rise of the motor shaft 24 being stopped. At this time, the rotor 41 can rotate in the other direction, and therefore the axial stopper 41b does not come in contact with the plate-like member 24c any more when the motor shaft 24 comes down by the rotation of the rotor 41 in the other direction. In this manner, the rotor can continue to rotate in the other direction, and the motor shaft can come down further.
Now operation is described. First, for starting from the state of the valve being fully closed, the coil 31 of the stepping motor 20 is energized in response to a pulsed voltage transmitted to the terminal 34 from a control unit (not shown) at the time of opening operation of the valve. Then the rotor 41 including the magnet 40 rotates stepwise in the direction of opening the valve. At this time, number of transmission pulses is coincident with that of steps, thereby enabling an accurate open-loop control. This stepwise rotation is converted into a liner movement by and with the female-threaded part 41a of the rotor 41 and the male-threaded part 24a of the motor shaft 24, and the motor shaft 24 moves in the direction of opening the valve (downward). At this time, the motor shaft 24 is assisted by the force of the assist spring 28 in the movement thereof. When the movement goes on and a top end surface of a tip portion 6a of the valve rod 6 comes in contact with a lower end surface of the motor shaft 24, the valve rod 6 comes down against an upward impetus exerted by the return spring 11 due to a drive force of the motor shaft 24. Furthermore, the valve 8, which is mounted on the lower end portion of the valve rod 6, also comes down with respect to the valve seat 5 to open the valve. Thus, the inlet 2 and the outlet 3 of the exhaust gas communicate with each other via the passage 4.
At the time of closing the valve, the operation reverse to the mentioned one is carried out. The rotor, which includes the magnet 40, rotates stepwise in the direction of closing the valve in response to a pulsed voltage transmitted from the control unit (not shown) to the terminal 34. This rotation causes the motor shaft 24 to move in the direction of closing the valve (upward). Following this movement, also the valve rod 6 rises by an upward impetus exerted by the coil spring 11, and then the valve 8 closes the opening of the valve seat 5.
The conventional mounting device for mounting the exhaust gas recirculation valve is constructed as described above, and therefore the stepping motor body and the valve body can be cooled with the cooling water introduced into the cooling water passage 13. However, since the cooling water passage 13 is formed around the valve housing 1, the valve body becomes large in size. Moreover, e.g., a piping for connecting the cooling water passage 13 to that of the engine system is required, which means that a water-cooling piping only for mounting the exhaust gas recirculation valve of complicated construction composed of a large number of parts is required. Hence, a problem exits in that the structure as described above brings about an increase in cost.
The present invention was made to solve the problems described above, and has an object of achieving a mounting device for mounting an exhaust gas recirculation valve capable of preventing a stepping motor, which drives and controls the exhaust gas recirculation valve, and a valve body from being over-heated due to an intense heat of the exhaust gas, and capable of reducing cost without requiring any cooling water piping for mounting the exhaust gas recirculation valve.
A mounting device for mounting an exhaust gas recirculation valve comprises: a valve housing that is connected and located in an exhaust gas reflux passage of an engine; a valve seat that is provided in an internal part of the mentioned valve housing; a valve rod that is mounted in an axially movable manner on the mentioned valve housing; a valve that is connected to the mentioned valve rod to be accommodated in the mentioned valve housing, and that moves in a direction of coming close to and in contact with the mentioned valve seat when the mentioned valve rod moves in one direction, as well as moves in a direction of being separate from the mentioned valve seat when the mentioned valve rod moves in the other direction; and a stepping motor that drives and controls the mentioned valve in a direction of opening or closing the valve via the mentioned valve rod;
the mentioned mounting device for mounting an exhaust gas recirculation valve being characterized in that a portion for mounting the mentioned valve housing on a cooling water circulating part for circulating cooling water from an engine block is provided in the mentioned valve housing, as well as the mentioned cooling water circulating part is constructed so that a part of a cooling water passage may be open at a portion of the mentioned valve housing being mounted thereon; and the mentioned valve housing is mounted on the mentioned cooling water circulating part, whereby the mentioned valve housing and the mentioned cooling water circulating part form the cooling water passage.
In the mounting device for mounting an exhaust gas recirculation valve of above construction, an intense heat of the exhaust gas can be absorbed in and radiated by circulating the cooling water taken out of the engine block or flowing into the engine block while bringing the cooling water into contact with the valve housing. As a result, the stepping motor driving and controlling the exhaust gas recirculation valve, and the valve body can be prevented from being overheated due to the intense heat of the exhaust gas without forming any additional cooling water passage around the valve housing of the exhaust gas recirculation valve. In this manner, reduction in cost can be achieved.
In the mentioned mounting device for mounting an exhaust gas recirculation valve according to the invention, it is preferable that a recess is provided in the area where the cooling water is in contact and circulates at a portion of mounting the mentioned valve housing on the mentioned cooling water circulating part; and that a protrusion is formed on the side opposite to the recess of the mentioned cooling water passage so that the cooling water is easy to flow into the recess side.
In the mounting device for mounting an exhaust gas recirculation valve of above construction, the cooling water passage is in the sate of getting into the valve housing of the exhaust gas recirculation valve. Accordingly, a surface area of the cooling water being in contact with the valve housing increases, thereby making it possible to enhance a cooling effect for the valve housing.
In the mentioned mounting device for mounting an exhaust gas circulation valve according to the invention, it is preferable that the portion where the cooling water is in contact and circulates is configured so as to have a smoothly curved surface along with a wall surface of the cooling water passage of the mentioned cooling water circulating part at the portion of mounting the cooling water circulating part of the valve housing.
In the mounting device for mounting an exhaust gas recirculation valve of above construction, resistance that occurs on the wall surface can be reduced during circulation of the cooling water, and residence area of the cooling water decreases. Therefore, not only the cooling effect for the valve housing can be enhanced but also a small strength of force is sufficient to circulate the cooling water. As a result, load on the cooling water pump can be reduced, making it possible to downsize the cooling water pump.
In the mentioned mounting device for mounting the exhaust gas recirculation valve according to the invention, it is preferable that a protrusion is provided in the area where the cooling water is in contact and circulates at a portion of mounting the mentioned valve housing on the mentioned cooling water circulating part.
In the mounting device for mounting the exhaust gas recirculation valve of above construction, a surface area of the cooling water being contact with the valve housing increases, making it possible to enhance the cooling effect for the valve housing.